1. Field of the Invention
The present invention relates to a semiconductor device with a protection function against ESD (electro-static discharge).
2. Related Art
An ESD protection element is typically connected between each of the input and output terminals and a reference voltage terminal VDD or VSS. The ESD protection element protects a semiconductor element from a breakdown being caused by electro-static discharge when an excessive positive or negative voltage is applied to an input/output terminal (refer to the Japanese Patent Laid-Open Publication No. 2002-124573). However, there are some semiconductor elements such as thermal diode, which use no pair of power source lines. In the case of connecting an ordinary ESD protection element to such an element, an additional power source line which is not related to the operation of the circuit element is necessary, thereby increasing the chip size and the number of pins. In order to avoid increasing the number of pins, it would be possible to connect the ESD protection element to a power source line which is used by another circuit block. In this case, however, noises can be supplied to the other circuit block, or on the contrary, the circuit element may undesirably suffer from noises caused by the other circuit blocks.